The invention relates to a method for localizing a drilling device of an earth drilling apparatus.
When introducing boreholes in the soil, it is typically necessary to control the exact drilling path. This requires localizing the drilling device within the soil to check if the drilling device follows the prescribed drilling path by comparing the actual position of the drilling device with its nominal position.
Control of the drilling path is particularly important when producing a horizontal borehole. In particular, horizontal boreholes are introduced in the soil in the context of trench-less installation and trench-less exchange of supply lines, for example freshwater and sewage lines, telecommunication cables, etc., and frequently extend from a starting pit to a destination pit. However, it is also known to introduce horizontal boreholes into the soil by initially drilling into the soil from the ground surface at an angle, whereafter the borehole is deflected into the horizontal direction, with the borehole continuing over the predetermined distance, until the drilling device again reaches a destination pit; alternatively, the drilling device can also be redirected after the horizontal section of the drilling path, this time towards the ground surface, so that the drilling device again exits the soil at the ground surface. It is evident that controllable drilling devices are required for producing a drilling path that is not straight. However, the use of controllable drilling devices may also make sense when a straight borehole should be drilled from the starting pit towards the destination pit; the drilling device frequently hits an obstacle during advance of the drilling device, for example a rock which cannot be penetrated, or an already existing supply line (e.g., water, gas or electricity line) which must not be damaged. In this situation, the obstacle must be “driven around” by diverting the earth drilling apparatus. However, this maneuver requires a precise localizing of the drilling device and in particular of the drilling head of this drilling device.
Several systems are known in the art which can be used to localize a drilling device of an earth drilling apparatus in the soil. The conventional systems have each a transmitter arranged inside the drilling head or in another section of the drilling device of the earth drilling apparatus, wherein the transmitter should be localized as closely as possible near the drilling head. The transmitter transmits a localization signal which is received by a receiver arranged above ground. The receiver evaluates the received localization signal to determine the position of the sensor and hence of the drilling head in the soil.
In one conventional system for localizing a drilling device, the drilling device has a magnetic dipole in the region of the drilling head which is rotatively driven together with the drilling device of the earth drilling apparatus. The magnetic field emitted by the magnetic dipole is measured by a receiver unit arranged above ground as a changing magnetic field, from which the position of the magnetic dipole and its orientation can be determined; the position and orientation of the drilling head can be directly determined due to the fixed arrangement between the magnetic dipole and the drilling head.
Other conventional systems based on the same principle for localizing a drilling device use a separate drive for the magnetic dipole, so that a localizing function can also be attained when the drilling device does not rotate.
Still other conventional systems use for producing the time-dependent magnetic field instead of a rotating magnetic dipole one or several coils to which an AC voltage is applied.
In the conventional systems, the transmitters arranged in the drilling devices are designed as active transmitters, i.e., they generate the corresponding localization signal either permanently without supply of an external signal or from energy (e.g., the aforedescribed system based on a permanent magnet), or the transmitters are supplied with electric energy and produce the localization signal by way of a corresponding conversion of the electric energy. The transmitters are typically supplied with energy from batteries. To eliminate the maintenance costs associated with changing the batteries, it has also been proposed to drive a mini-generator arranged in the drilling head with the flushing fluid which is provided anyway and introduced into the soil to improve the advance of the drilling device and to flush the drilling debris out of the borehole.
The conventional systems are technically complex and can retrofitted into existing drilling devices of earth drilling apparatuses either not at all or only at significant costs. Systems including electrical components (e.g., the rotary drive for the magnetic dipole, a coil, etc.) are frequently also susceptive to malfunction, because the electrical components can be damaged by the vibrations and impacts that are present during the drilling operation.
Based on this state-of-the-art, it was the object of the invention to provide an improved method for localizing a drilling device of an earth drilling apparatus which ameliorates these disadvantages. In addition, a corresponding system for localizing a drilling device of an earth drilling apparatus is provided.